Title VI of the U.S. Clean Air Act of 1990 enacts the U.S. strategy for complying with the Montreal Protocol for protection of Earth's stratospheric ozone layer.9 Title VI is administered by the Stratospheric Protection Division within the Office of Air and Radiation. Section 612 of Title VI directs EPA to set up the Significant New Alternatives Policy (SNAP) program, to evaluate any halon substitutes or alternative fire protection technologies to ensure that they reduce the overall risk to human health and the environment and to promote these substitutes to achieve rapid market acceptance. EPA's goal is to ensure that industry and consumers have ample choices for the diversity of applications in which CFCs and halons are currently used.
EPA adopted a risk-balancing approach on health and safety issues by looking at likely exposure pathways in use of a substitute agent in each sector. The risk to individuals from exposure to halon substitutes is generally from discharges that occur infrequently. Chronic effects from exposure to halon substitutes are not usually a concern, because when used, these substances are discharged in high concentrations over short periods of time and thus potentially present an acute hazard. Risk from exposure to halon substitutes is accordingly best assessed by analysis of acute toxic effects associated with exposure to these compounds, such as developmental toxicity and cardiotoxicity. In most instances, cardiotoxicity occurs at lower levels than does fetotoxicity, and therefore, unless otherwise warranted by the developmental data, EPA bases the estimates for emergency exposure limits during halon use on the no observable adverse effect level (NOAEL) and lowest observable adverse effect level (LOAEL) reported for epinephrine-sensitized cardiotoxicity in dogs (and in a few instances monkeys). Human heart arrhythmias and sudden death resulting from overexposure to CFCs, halons, and other halogenated and non-halogenated hydrocarbons have been documented in work-place settings and in volatile substance abuse (e.g., glue sniffing).10
To assess the safety of a fire extinguishing agent for use in a total flooding system, EPA analysts examine the actual design concentration as NFPA defines it,11 i.e., the cup burner extinction concentration plus 20%, or in some cases the actual large-scale testing design concentration, and compare this value to levels at which cardiotoxic effects have been observed.
The situation differs for streaming agents (i.e., chemicals applied to localized fires, usually by being propelled from an extinguisher) because such use is a localized application, and air exchange further dilutes the concentration of the agent. EPA requires manufacturers to submit data acquired by personal monitoring for the anticipated usage. The results of these tests show that actual exposure is much lower than what the models predict. Consequently, EPA has listed agents as acceptable, even with a LOAEL as low as 1.0 or 2.0%.12
The conditions stipulated under SNAP for use of total flooding agents are patterned after current Occupational Safety and Health Administration (OSHA) requirements for use of halon 1301 (CF3Br) systems. Because OSHA does not currently specify acceptable levels of exposure to substitute fire extinguishing agents, EPA is laying these values out very specifically and has initiated efforts to work with OSHA as that agency takes steps to amend its regulation of fixed gaseous extinguishing systems (OSHA Regulation 1910.162).
When considering environmental effects of halon substitutes, EPA first looks at ozone depletion potential to determine if a substance could significantly damage the stratospheric ozone layer. Any class I substance (ODP of 0.2 or higher) must be phased out of production in the United States within 7 years of listing. While the Clean Air Act does not explicitly define a class II substance, by implication it is an agent with an ODP of less than 0.2. Currently the chemical with the lowest ODP that EPA has listed as a class II substance is HCFC-123 (CF3CHCl2), with an ODP of 0.02.
While EPA considers other environmental impacts besides ozone depletion potential (including aquatic toxicity, air pollution, and so on), global warming potential (GWP) and atmospheric lifetime are the key additional issues in evaluating halon substitutes. Action number 40 of President Clinton's Climate Change Action Plan, released in November 1993, directs EPA to minimize unnecessary emissions of greenhouse gases to help meet the national goal of reducing emissions in the year 2000 to 1990 levels. EPA again has adopted an approach that seeks to balance the risk posed by ODP and GWP and the related atmospheric lifetimes of these agents.